Gas turbine engines are known to include a compressor for compressing air; a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas to extract shaft power. The combustion process in many older gas turbine engines is dominated by diffusion flames burning at or near stoichiometric conditions with flame temperatures exceeding 3,000° F. Such combustion will produce a high level of oxides of nitrogen (NOx). Current emissions regulations have greatly reduced the allowable levels of NOx emissions, requiring improvements in combustors to reduce undesirable NOx production.
Gas turbine engines using annular combustion systems typically include a plurality of individual burners disposed in a ring about an axial centerline for providing a mixture of fuel and air to an annular combustion chamber disposed upstream of the annular turbine inlet vanes. The combustion process of the several burners will interact in the combustion chamber since all burners discharge the combustible mixture to the single annulus. Consequently, combustion processes in one burner may affect the combustion processes in the other burners. Other gas turbines use can-annular combustors wherein individual burner cans feed hot combustion gas into respective individual portions of the arc of the turbine inlet vanes. Each can includes a plurality of main burners disposed in a ring around a central pilot burner, as illustrated in U.S. Pat. No. 6,082,111. Can annular combustors are generally more expensive to fabricate as a result of the use of multiple burners within each of the multiple combustor cans which may include cross flame tubes connecting combustor baskets.
The demand to decrease exhaust emissions continues, thus improved techniques for economically controlling the combustion conditions of a gas turbine engine are needed.